The present invention relates to a clock generating device, and further relates to an electronic circuit, an integrated circuit and electrical machinery that incorporate the clock generating device. In particular, the present invention relates to a clock generating device for performing processing in synchronization with a clock signal generated by an oscillator provided externally, and an electronic circuit, an integrated circuit, and electrical machinery that incorporate the clock generating device.
An electronic circuit that performs processing in synchronization with a system clock signal generated by an externally provided oscillator (hereinafter also referred to as “external oscillator”) is known. Since external oscillators are constructed using, for example, a crystal vibrator, frequency accuracy is high, but the external oscillators are not protected by a package, so there is a possibility of failure due to dust or the like. If the external oscillator fails, the electronic circuit cannot operate and cannot notify an external microcomputer of the error, for example.
As an example, Patent Literature 1 discloses a semiconductor integrated circuit that performs processing in synchronization with a system clock signal generated by an external oscillator. The semiconductor integrated circuit further includes an oscillator (hereinafter referred to as “internal oscillator”) provided therein. With the semiconductor integrated circuit, when an abnormality of the external oscillator is detected, a system clock signal is generated by the internal oscillator.
As a result, the semiconductor integrated circuit can operate continuously using the system clock signal generated by the internal oscillator even if an abnormality occurs in the external oscillator.